1. Field of the Invention
The present invention relates generally to an expansion bolt, and in particular to an internal driving expansion bolt comprising a spherical member for expanding a sleeve in a low-resistance and smoothly operating manner.
2. The Related Art
Expansion bolts are classified as external driving type and internal driving type. Both types of expansion bolts require “force impact” on an end of the bolt to expand a sleeve. The “force impact” that hits the bolt cannot be well controlled and may sometimes cause cracking of a wall in which the expansion bolt is fixed. In addition, since, after the impact, most of the bolt is completely received in the hole formed in the wall, there is no way for an observer to inspect if the bolt is properly mounted, which may lead to potential damage in applying a great load to the bolt. Further, an internal driving type expansion bolt requires a tool extending into the bolt for transmission of the “force impact” to the bolt. Threading formed inside the bolt is often damaged by the tool during the process of impacting.
In Taiwan Patent Publication No. 345247 that is issued to the present inventor, an expansion bolt is disclosed, comprising an inner-threaded sleeve defining a tapering hole in which a cone is movably received. A driving element is received in the sleeve for engaging the cone and threadingly engaging the inner threading of the sleeve. By screwing the driving element in the sleeve, the driving element axially drives the cone through the tapering bore in the sleeve thereby radially expanding the sleeve. A disadvantage of the conventional design is the great friction force induced when the cone is driven close to the smaller diameter end of the tapering bore. This is due to the great contact area between the cone and tapering bore.
Taiwan Patent Publication No. 390394, also issued to the present inventor, discloses an expansion bolt wherein the driving element is integrally formed with the cone so that a unitary driving and expanding member is movably received in the sleeve. Due to the same reasons, the unitary driving and expanding member is subject to a great friction force when it is moved close to the smaller diameter end of the tapering bore. In addition, since the sleeve of the expansion bolt is generally not made of high precision, the unitary driving and expanding member is subject to undesired eccentricity with respect to the sleeve to some extents. This makes it more difficult in driving the cone in a smoothly operating manner.
Thus, it is desired to have an expansion bolt that overcomes the above-discussed problems.